Our studies have evaluated biochemical changes in placentas from humans exposed to rice oil contaminated with polychlorinated biphenyls (PCBs) and polychlorinated bidenzofurans (PCDFs) in Taiwan. Placentas were obtained from non-smoking women four to five years after the exposure had occurred. The exposed individuals ingested approximately 1-3g PCBs and 5mg PCDFs, and many exhibited symptoms characteristic of PCB poisoning. This disease was termed Yucheng in Chinese. We examined a number of parameters including arylhydrocarbon hydroxylase (AHH) activity, cytochrome P-450 isozymes, epidermal growth factor (EGF) receptor binding properties and actions and Ah receptor. We also quantified concentrations of PCB and PCDF congeners known to be present in the contaminated rice oil. Our results revealed a dramatic elevation in placental AHH activity in samples from PCB-PCDF exposed women. This increase was associated with a parallel increase in placental microsomal protein immunochemically-related to cytochrome P-450 form 6. Placental cytosol preparations were examined for 3H-TCDD binding capacity by standard receptor techniques. EGF receptor- mediated autophosphorylation capacity was significantly diminished in PCB-PCDF placentas but this effect was not associated with changes in plasma membrane EGF receptor binding properties (Kd and Bmax). The EGF receptor autophosphorylation effect correlated well with the decrease in birthweight observed in offspring of exposed women suggesting that this biochemical event might provide a good "marker of effect" for the toxic halogenated aromatics. Two PCDF congeners (2,3,4,7,8-penta CDF and 1,2,3,4,7,8-hexa CDF) were detected in Yucheng placentas but not controls. Several PCBS were also detected (including the 2,2',4,4',5,5',-hexa CB and 2,3,3',4,4',5-hexa CB) in much higher concentrations in Yucheng placentas. Surprisingly, placental concentrations of PCBs correlated better with effects than did the PCDFs.